The WHTC test is a transient engine dynamometer schedule defined by the global technical regulation (GTR) No. 4  developed by the UN ECE GRPE group . The GTR is covering a world-wide harmonized heavy-duty certification (WHDC) procedure for engine exhaust emissions. The regulation is based on the world-wide pattern of real heavy commercial vehicle use.
Two representative test cycles, a transient test cycle (WHTC) with both cold and hot start requirements and a hot start steady-state test cycle (WHSC), have been created covering typical driving conditions in the EU, USA, Japan and Australia. WHTC testing requirements were adopted for the first time by the Euro VI emission regulation for heavy-duty engines.
The WHTC is a transient test of 1800 s duration, with several motoring segments. Normalized engine speed and torque values over the WHTC cycle are schematically shown in Figure 1.
Figure 1. World Harmonized Transient Cycle (WHTC)
Note: Negative torque values are arbitrary representation of closed rack motoring
A chassis dynamometer version of the test, the World Harmonized Vehicle Cycle (WHVC), has also been developed, but is not a part of standard international testing procedurs.